Remilia Scarlet is the owner and head of the Scarlet Devil Mansion, the mistress of Sakuya and Meiling, and the older sister (and guardian) of Flandre. Though her appearance (and often behavior) is childlike, and seems nonthreatening, she has fearsome magical powers and a reputation to match, being known throughout Gensokyo as the dangerous "Scarlet Devil." Like all vampires she is photosensitive and weakens when exposed to sunlight, so she typically remains inside her mansion (which has few windows to prevent light getting in) during the day and emerges during the night. While she is naturally known to drink human blood, her light appetite means her victims almost never die from their wounds.

While her behavior is usually self-centered and somewhat bratty, it is possible to befriend her, however, humans and youkai alike prefer to avoid her. Her name, appearance, house, and clothing all indicate she is European in origin and emigrated to Japan many years ago (Her reason is unknown). She claims to be a descendant of the world's most notorious vampire, Count Vlad Ţepeş Dracul, but this is a bald-faced lie.

Story

In Embodiment of Scarlet Devil, Remilia decided to release a mist over Gensokyo to block out the sun and let her move freely during the day; after her scheme was discovered and halted, she was forced to use a parasol to shade herself when she wanted to move around during daylight hours (as mentioned in Immaterial and Missing Power). In Imperishable Night she headed out to punish the ones who took the full moon from the night sky since the fighting would be at night. In Scarlet Weather Rhapsody, she settles her "own" investigation by ordering Sakuya to drag the suspects to her, in order to find the culprit, figuring later that the culprit is above the mountains, where she is very prone to the light.
In Silent Sinner in Blue, she built a rocket to get to the moon.